I still don't understand why this needs to be standardised upon,
particularly since Common Lisp pathnames in general are so
subfunctional. (Just what can portable programs do with the damn things
after they have successfully read them?)
Even if others do feel an urgent need to allow such portablability, I
don't understand why #S(PATHNAME ...) syntax isn't acceptable. (Perhaps
because Pitman hadn't `invented' it yet.)
One could go with #S(PATHNAME "host:namestring")
or #S(PATHNAME "host" "namestring"), which is perhaps the best choice,
or #S(PATHNAME :host "host" :directory '("foo" "bar") :name "baz")
or whatever.
Usurping #P makes it harder for users to find an unused reader macro
character.